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Flood Control Structures Addressing Climate Change Impacts on Infrastructure: Preparing for Change

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Flood Control Structures Addressing Climate Change Impacts on Infrastructure: Preparing for Change FACT SHEET FLOOD CONTROL STRUCTURES ADDRESSING CLIMATE CHANGE IMPACTS ON INFRASTRUCTURE: PREPARING FOR CHANGE Flood control structure in Iloilo, Philippines. Photo Credit: IRG Changes in climate will threaten the efficacy, adequacy, and durability of flood control structures and their continued services. FLOOD CONTROL STRUCTURES INCLUDE: • Dikes Since flood control structures provide defense against frequent, • Spurs small floods in rivers and estuaries, rising sea levels, and storm surges, • Levees climate change impacts on these structures may significantly affect the • Seawalls communities relying on their protection. Such impacts have implications for urban stability, economic growth and trade, and food and water availability. FLOOD CONTROL STRUCTURES SUPPORT: • Urban programs These structures and their services can be protected with adaptation • Economic growth and trade strategies that include fortifying existing structures and updating design • Food and water availability standards to accommodate future climate changes. FLOOD CONTROL STRUCTURES ARE development practitioners can help ensure the lasting effects of INTEGRAL TO DEVELOPMENT PRIORITIES development projects and programs in vulnerable areas. Flood control structures are designed to protect coastal and river-bank CLIMATE STRESSORS CAN SIGNIFICANTLY areas, including urban and agricultural communities, homes, and other IMPACT FLOOD CONTROL STRUCTURES economically valuable areas, and the people located within them. These structures are used to divert flows of water, by re-directing rivers, slowing AND THEIR SERVICES natural changes in embankments and coastlines, or preventing inundation Like many other types of infrastructure, flood control structures are of vulnerable coastlines or floodplains. Dikes, spurs, levees, and seawalls often designed to last several decades. Several climate stressors affect often act as the first line of defense against overflowing rivers, floods, the efficacy and durability of flood control structures, including changes in storm surges, and—in the longer term—rising seas. By keeping water out, precipitation, sea levels, extreme events, and resulting storm surges. Flood flood control structures lessen harm to physical infrastructure and help to control structures are unique in that they can be compromised by the ensure continuation of communities’ economic and social activity. same stressors they are designed to withstand. For example, increases in the intensity and frequency of floods could overwhelm these structures, But flood control structures do not completely eliminate risk. Flooding causing them to fail. These stressors will grow in importance as climate may occur if the design water levels are exceeded. If poorly designed, change continues to alter their intensity, variability, and accompanying constructed, operated or maintained, these structures can increase risk hazard potential. by providing a false sense of security and encouraging settlements or economic activity in hazard-prone areas. Potential impacts will depend on a variety of factors that affect the vulnerability of these structures. For example, if sea walls are constructed Nevertheless, many development programs rely on these structures to in areas that are experiencing land subsidence, they will be more maintain program objectives, including continued food and water supplies, vulnerable to storm surges and sea level rise. Climate change risks vary economic activity, and protection from storms and floods. For example, in relative importance, with a range of cost implications, compounding urban initiatives (e.g., urban transport projects) in coastal cities like Dhaka, effects, and impacts on development objectives. Failures of flood control Bangladesh necessarily rely on effective flood control structures, such structures can result in dire consequences for the services provided as pump stations and dikes, to maintain program effectiveness in the and investments made by the development community. Table 1 provides short-term. By supporting the climate-resilient design, construction, several examples of potential climate change impacts on flood control and maintenance of flood control structures, USAID and other structures. ADDRESSING CLIMATE CHANGE IMPACTS ON INFRASTRUCTURE: PREPARING FOR CHANGE FLOOD CONTROL STRUCTURES 1 Table 1. Examples of Potential Climate Change Impacts on Flood Control Structures and Services Flood Control Structures and Services Precipitation Change • Failure of existing flood control structures due to increased flooding from increased precipitation • Weakened embankments or inefficient impervious core due to erosion and liquefaction from recurring, intense flooding Sea Level Rise • Overflowing of older structures built to standards that do not integrate sea level rise • Weakening of flood control structures due to land subsidence and erosion combined with sea level rise • Inundation of structures in low-lying lands due to failure of flood control structures Storm Surge • Overpowering of structures due to increased height of waves, tides, and surges • Weakened or damaged structures (e.g., cracks in critical junctures) due to repeated storm surge Extreme Events • Damage to and destruction of flood control structures due to sudden freeze-thaw cycles or the combined forces of cascading extremes such as cyclones, snowmelt, heavy precipitation • Breaches of structure leading to temporary and permanent inundation DEVELOPMENT PROGRAMS CAN INCLUDE addition to hydrologic, environmental, and ecosystem impacts. Adaptation actions should be integrated into the overall risk management strategy for FLOOD CONTROL STRUCTURE-RELATED flood control structures. ADAPTATION Adaptation priorities should be selected based on decision-makers’ To reduce climate change impacts on flood control structures and the assessment of the following four key factors (presented with illustrative resulting damage and destruction to coastal and low-lying communities, question; refer to Overview for further guidance): development practitioners must adapt flood control structures to future climate stressors. Adapting flood control structures will protect • Criticality – What is the hazard potential of failure of these investments in a variety of sectors, including transportation, energy, and structures, including population and value of assets in the area urban programs. protected by the structures? The resilience of flood control structures can be increased in many ways. • Likelihood – Given climate projections, how likely is it that this For example, flood control structures should be built to higher levels structure will be weakened or overwhelmed by climate change? and with more resilient materials and designed to withstand repeated • Consequences – Will climate changes lead to breach, overtopping, or and more extreme floods. Similarly, in designing flood control structures, complete failure of these structures or destabilize the embankments? If USAID and other development organizations should consider, where the structure fails, what damage and destruction will ensue? feasible, constructing back-up structures to provide services in case of • Resources available – Can the structure be fortified at low cost? failure. In addition, design standards should incorporate sea level rise Do new structures need to be built to provide adequate protection projections, as well as the hydrology and physiography of the watershed to services? Are there certified specialized engineers to design, construct, minimize or avoid unintended adverse impacts. inspect, and maintain these structures in the target areas? It is critical that trained and registered engineers design, implement, and An integrated, climate-resilient approach to flood control management review new construction and improvements to ensure stability, since will ensure that development program outcomes are durable and untested flood control structures may constitute a direct threat to human long-lasting. Climate change projections should be deliberately and life. In addition, communities should avoid promoting an unfounded sense knowledgeably included in the various project cycle stages, including the of security as any structure may fail in extreme circumstances. design, construction, and maintenance of flood control structures. Different To understand the implications for flood control structures, decision options exist to mitigate the impacts of these climate stressors, including makers should identify plausible future climate scenarios to understand structural changes (e.g., changes to embankment slopes) and policy how relevant factors—such as sea levels and extreme event intensity— changes (e.g., changes to zoning codes, relocation, designing redundancy are projected to change. Using this information, decision makers can plans). Table 2 provides illustrative examples of adaptation options for identify needed changes to the design, construction, and maintenance of flood control structures, and shows the overall approach to assessing and structures. Development practitioners must understand the vulnerabilities addressing climate risks using the Climate-Resilient Development (CRD) of different structures, based on location, design, and construction in Framework. See the Overview for further guidance. 2 FLOOD CONTROL STRUCTURES ADDRESSING CLIMATE CHANGE IMPACTS ON INFRASTRUCTURE: PREPARING FOR CHANGE Table 2. Examples of Flood Control-Related Actions by Project Cycle Stage Project Cycle Stage Project Cycle Actions • Identify
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